This invention relates to liquid-level detectors and to reservoirs including such detectors.
Liquid-level detectors are required in many applications, such as, in engines to provide a warning indication when the quantity of oil or fuel reaches a low level. Detectors of many different constructions have been used in the past but these have various disadvantages and limitations. For example, with previous arrangements it has usually been necessary to mount the detector within the liquid container, thereby presenting problems in making a seal where the detector cable emerges from the container. Installation, checking and maintenance of such detectors is also difficult and, furthermore, they can be damaged by contact with the liquid or, if electrically operated, present a hazard with flammable liquids. For this reason, it is desirable to mount the detector externally of the container, especially where the detector is to be added to existing containers. One example of previous detectors of this kind relies on the interruption or completion of a beam of light directed across the container at the height at which the warning indication is to be provided. These detectors, however, require two windows on opposite sides of the container through which the light emitter and sensor respectively can view one another. Many existing containers have only one window, for visual inspection of liquid level, making this method of detection unsuitable. Problems also arise, especially where the detector is to be used with an engine, such as a gas-turbine engine, in providing and mounting a detector to withstand the adverse environment--high vibration and temperature changes.